1. Field of the Invention
The present invention relates to a movable light-source type exposure apparatus, which enables an image pattern of an original to be baked with high precision onto a material to be exposed, such as a print board, by use of parallel lights.
2. Description of the Prior Art
A conventional exposure apparatus is arranged such that a point light source is disposed at a focal point of a deep parabolic reflector. A light-shielding member is disposed between the light source and an exposure plane so as to obtain parallel light rays. An original and the material to be exposed are caused, in a state wherein both are cohered together, to move along the exposure plane by use of a conveyor means or the like. Whereby, any point on the material to be exposed is exposed with a specified cumulated amount of light by the shadow produced by the light-shielding member.
In the above-mentioned exposure apparatus, however, since an actual light source is not a point in its true meaning but is of some measurable size, there are produced scattered light rays. For this reason, it was necessary to dispose the light-shielding member at a position closer to the material to be exposed in order to obtain a more precise exposure thereof. For this reason, the light-shielded zone was comparatively small. So that, in order to obtain a required area of exposure, one had to make the light-shielding member large in size and dispose the material to be exposed at a position spaced away from the light source. As a result, the efficiency with which light rays were utilized decreased and necessitated the use of a deep parabolic reflector capable of providing a high light-collecting efficiency.
In the conventional movable type exposure apparatus, the original pattern is not required to be finely baked onto the material to be exposed with high precision. In order to make the apparatus more efficient with respect to productivity as well as to make it easier to construct, the exposure apparatus was arranged such that the light source was fixed and the original and the material to be exposed were moved along the exposure plane in a condition wherein both were cohered to each other.
In recent years, integrated circuits have increased in their degree of integration, in number of pins employed, and in amount of wiring. On the other hand, an integrated circuit which is small in pin interval has more frequently been desired. For this reason, a correspondingly fine print board has also been demanded. Conventional exposure apparatus has, however, failed to provide an exposure precision which meets such requirements. A reason for this is that while the precision with which an original image is positioned relative to a material to be exposed has at present been required to be .+-.5 microns, the exposure apparatus adapted to transfer the original and the material to be exposed in a state wherein both are cohered together has failed because of mutual displacement therebetween due to vibration at transfer. A second reason is that since the conventional deep parabolic reflector has a short focal point, the parallel light rays are more scattered, as compared with a small-width parabolic reflector of longer focal point, when a light source of same size is used. This causes a decrease in clarity of the image, resulting in a decrease in the exposure precision.